Much development is being achieved on the micrometer (μm) and nanometer (nm) size scales in the fields of biology, medicine, physics, chemistry, electronics, engineering, and nanotechnology to, for example, study objects (e.g., materials, organisms, viruses, bacteria, etc.), create new objects, and/or assemble objects together with great precision.
To perform manipulation of objects on such a small size scale, it is often necessary to use microscope equipment to aid in observing the objects. For instance, the smallest object that human beings can see with the unaided eye is about 0.1 millimeter (mm). With a good light microscope (also referred to as an “optical microscope”), an image may be magnified up to about 1500 times. However, magnification achievable with light microscopes is limited by the physics of light (i.e., the wavelength of light) upon which the operation of such microscopes is based. For example, light microscopes have relatively limited resolving power (ability to distinguish clearly between two points very close together) and the best resolving power that can be achieved with a light microscope is around 0.2 μm. Points closer together than this cannot be distinguished clearly as separate points using a light microscope.
Electron microscopes have been developed that use a beam of electrons, rather than light, to study objects too small to study with conventional light microscopes.
Modern electron microscopes can view detail at the atomic level with sub-nanometer resolution (e.g., less than 0.1 nm resolution) at up to a million times magnification.
Various different types of electron microscopes have been developed. One type of electron microscope is the transmission electron microscope (TEM). In a TEM, electrons are transmitted through a thinly sliced specimen to be observed and typically form a viewable image on a fluorescent screen or photographic plate. Areas of the specimen having relatively higher density generally appear darker in the resulting image. TEMs can magnify, an object under observation up to one million times and are used extensively, in the fields of biology and medicine for example, to study structures of viruses and plant and animal cells.
Another type of electron microscope is the scanning electron microscope (SEM). In an SEM, the beam of electrons is focused to a point and scanned over the surface of the specimen. Detectors collect the backscattered and secondary electrons coming from the surface and convert them into a signal that in turn is used to produce a highly realistic, three-dimensional image of the specimen. SEMs generally require the observed specimen to be electrically conductive. Specimens that are not conductive are typically coated (e.g., using a sputter coater) with a thin layer of metal (often gold) prior to scanning. SEMs can magnify up to around one hundred thousand times or more.
Another type of microscope is the focused ion beam (FIB). The FIB is now commonly used for the preparation of specimens for later analysis using a transmission electron microscope (TEM).
The focused Ion Beam (FIB) system uses a gallium ion beam to raster over the surface of a sample in a similar way as the electrons beam in a SEM. The generated secondary electrons (or ions) are collected to form an image of the surface of the sample.
Unlike SEM, the FIB is inherently destructive to the sample. When the FIB gallium ions strike the sample, they cause atoms on the surface of the sample to sputter. Thus, the FIB is commonly used as a micromachining tool, to modify or machine materials on the microscale and nanoscale. For example, the FIB is often used in the semiconductor industry to patch or modify existing semiconductor devices. The FIB is also commonly used to prepare material samples for observation with a TEM, which requires very thin samples, i.e. samples of less than about 100 nanometers in thickness.
Structural evaluation using an electron microscope, such as a SEM or a TEM, has been conventionally employed as one of methods for examining and evaluating semiconductor devices and other engineering materials.
The failure analysis of semiconductor devices now routinely requires resolution requirements that only a TEM can achieve from samples prepared with an FIB instrument. Procedures have been developed for obtaining samples cut from a semiconductor device. Typically, a sample is from an original wafer or bulk material, prepared with the FIB, mounted to a substrate, for example a TEM grid using micromanipulation techniques, and sometimes further processed using the FIB. Specially designed TEM grids are commercially available from Omniprobe, Inc., Dallas, Tex., and other sources. TEM grids are typically made of copper, but other TEM grid materials include molybdenum, aluminum, nickel, and beryllium.
The preparation of samples using an FIB involves considerable cost because of the time of preparation and the high capital expense of the processing instruments. Further, TEM grid mounted samples are prone to breakage and damage due to the delicate structures of the materials mounted on the grid, as well as the fragile structure of the grid itself. Holders, for example, TEM grid boxes, have been developed for holding TEM grid-mounted samples, but none have proven to be adequate in protecting the samples from breakage, damage or loss, for example, during handling or during transportation. The TEM grids themselves are usually very thin, typically on the order of 25-30 μm. Even very minor flexing of the grid can endanger the sample mounted thereto. Membrane boxes are available which are designed to support a TEM grid mounted sample between two thin, flexible sheets of polymer. However, these membrane boxes have been known to cause damage to samples.
There is a continuing need for more effective assemblies for holding, storing and/or protecting microscopy samples.